A satellite positioning system (hereinafter referred to as a global navigation satellite system (GNSS)) that determines a current position and speed by receiving signals from satellites includes a global positioning system (GPS) by the United States, a global orbiting navigation satellite system (GLONASS) by Russia, a BeiDou by China, a Galileo by the EU, and a quasi-zenith satellite as a complementary satellite by Japan, for example.
Electronic equipment that uses the GNSS includes, for example, car navigation equipment with a GPS receiver mounted thereon. Basic functions of the GPS receiver are to receive signals from four or more GPS satellites, to calculate a position of the receiver from the received signals, and to inform a user. In other words, the GPS receiver acquires orbital data of the satellite by demodulating the signal from each satellite and then, by a system of equations, derives a three-dimensional position of the receiver from an orbit and time information of the satellite and delay time of the received signal. Since there is an error between time in the GPS receiver and time in the satellite, four receiving satellites are required to eliminate influence of such error.
In recent years, the importance of positional information has been increasing, and the positional information has becoming necessary even indoors. However, even if sensitivity of the GNSS receiver becomes high, a signal that can be received from the GNSS satellite indoors (hereinafter also referred to as a GNSS signal) is considerably weak, and the signal that can be received is not a direct wave from the GNSS satellite. Therefore, the GNSS signal may not be able to be received, or even if it is possible to receive the signal, it becomes difficult to use such signal due to a large positioning error.
Accordingly, in recent years, there have been proposed several positioning methods that do not use the GNSS signal indoors. For example, there has been proposed a method of specifying a position by receiving a MAC address, which is unique information of a fixed access point of a wireless LAN, and acquiring an installed position of the fixed access point from such unique information (for example, see Non-Patent Document 1).